var climbStairs = function(n) {
  const dp = new Array(n + 1).fill(0);
  dp[1] = 1;
  dp[2] = 2;

  for (let i = 3; i <= n; i++) {
    dp[i] = dp[i-1] + dp[i-2]
  }
  return dp[n];
}

console.log(climbStairs(3))